1. Field of the Invention
The present invention relates to object verification, and more particularly, to an object verification apparatus and method in which, when a verification process is performed by applying a plurality of matching algorithms on a query image of an object, each matching algorithm is performed in consideration of color information, adaptive score normalization is performed on the query image, or a weight of a score obtained from each matching algorithm is estimated based on an equal error rate (EER), thereby enhancing the performance of the verification process using a fused score.
2. Description of the Related Art
Objects, for examples, biometric features which have been recently been widely used or intensively studied, include face and its thermogram, fingerprint, hand geometry, hand vein pattern, iris characteristics, retina pattern, signature and handwriting, and voice. However, all of these biometric features have their positive and negative points, and none is clearly superior in terms of all the generally required qualities, i.e. universality, uniqueness, permanence, collectability, performance, acceptability, and circumvention. That is, each biometric feature may have a vulnerable environment or user.
Most of the promising application fields of biometrics, such as information security, financial services, criminal identification and governmental civil service, require a very low error rate, which is difficult to achieve with verification technology based on a single biometric feature. Accordingly, multimodal biometrics technology is being developed, with the goal of enhancing performance and reliability by combining a number of biometrics methods.
A multimodal biometric system may have various operation scenarios. First, a single biometric feature may be obtained using different types of sensors. For example, optical, ultrasonic, and semiconductor sensors may be used to obtain fingerprints. Second, a plurality of different biometric features may be used. For example, a face and fingerprints can be used for biometric recognition. Third, a plurality of feature units may be used for a single biometric feature. For example, the irises of both eyes, the images of both hands, and the ten fingerprints of all fingers may be used. Fourth, a single biometric feature may be obtained several times using a single sensor. For example, the fingerprint of one finger may be obtained several times, the voice of the same person may be sampled several times, or the same person may be photographed several times. Fifth, after an input biometric feature signal is represented in various ways, various matching algorithms may be used. For example, various biometric features may be extracted in response to a fingerprint signal, and biometric recognition may be performed using various matching algorithms.
The level of fusion of a system using multiple information sources denotes the level of information processing at which information is actually fused. Information fusion may occur at a number of levels, such as a feature extraction level, a matching score level, or a decision level, within a multimodal biometric system. Therefore, the level at which information is to be fused must be determined. In particular, there are some considerations that need to be made in order to fuse score matrices obtained from a plurality of matching units into a single score matrix. First, the score matrices are not homogeneous. For example, a matching unit may output a dissimilarity measure as distance, and another matching unit may output a similarity measure. Second, the outputs of the matching units may not use the same scale, range or units. Third, the score matrices obtained from the matching units may follow different statistical distributions. For this reason, it is essential to perform score normalization to convert the score matrix of each matching unit to a common format, before the matrices are fused.
However, a conventional score normalization algorithm has the following problems. First, since a score matrix is obtained using a grayscale image instead of a color image, the accuracy of the score matrix is reduced. Second, score normalization is dependent on the score matrix, so a different normalization parameter is used for each score matrix. Therefore, since the same normalization parameter is used for all scores in a score matrix, the increase of the verification rate is limited. Third, fusion weights used to fuse the normalized score matrices may be manually determined in advance. Alternatively, the fusion weights may be determined based on false acceptance rate (FAR)-false rejection rate (FRR), linear discriminant analysis (LDA), or a recognition rate. Therefore, the actual performances of the matching units are not properly reflected in the fusion weights, which reduces the accuracy of the fusion weights.
Multimodal biometric systems are disclosed in U.S. Pat. Nos. 6,651,057 and 6,539,352, and a paper entitled “Score Normalization in Multimodal Biometric Systems,” Pattern Recognition, 2005, by Anil Jain, Karthik Nandakumar, and Arun Ross.